Showing papers in "IEEE Microwave Magazine in 2014"

Harvesting Wireless Power: Survey of Energy-Harvester Conversion Efficiency in Far-Field, Wireless Power Transfer Systems

Abstract: The idea of wireless power transfer (WPT) has been around since the inception of electricity. In the late 19th century, Nikola Tesla described the freedom to transfer energy between two points without the need for a physical connection to a power source as an ?all-surpassing importance to man? [1]. A truly wireless device, capable of being remotely powered, not only allows the obvious freedom of movement but also enables devices to be more compact by removing the necessity of a large battery. Applications could leverage this reduction in size and weight to increase the feasibility of concepts such as paper-thin, flexible displays [2], contact-lens-based augmented reality [3], and smart dust [4], among traditional point-to-point power transfer applications. While several methods of wireless power have been introduced since Tesla?s work, including near-field magnetic resonance and inductive coupling, laser-based optical power transmission, and far-field RF/microwave energy transmission, only RF/microwave and laser-based systems are truly long-range methods. While optical power transmission certainly has merit, its mechanisms are outside of the scope of this article and will not be discussed.

Substrate Integrated Waveguide Filter: Basic Design Rules and Fundamental Structure Features

Abstract: The electromagnetic (EM) spectrum is becoming more crowded, and it is densely populated with various wireless signals and parasitic interferers in connection with communication and sensing services. Increasingly sophisticated radio-frequency (RF), microwave, and millimeter-wave filters are required to enable the selection and/or rejection of specific frequency channels. This will occur in future generations of the wireless system, such as the current hotly debated fifth-generation communication systems, where the spectral channelization of a heterostructured wide-band signals will be critical in support of a host of coexisting bandwidths or speeds and applications. Bandpass filters have been the most useful and popular types for such applications and are the most difficult to design and develop in practice. Other types of filters such as notch (stopband) and lowpass filters have also been widely used in many systems, and their design is generally perceived less critical with respect to band-pass filters. This article will focus on the presentation and discussion of bandpass filters. Design factors or parameters of filters, such as selectivity, cost, miniaturization, sensitivity to environmental effects (temperature and humidity, for example), and power handling, combined with predefined in-band and out-of-band performance metrics, are critical specifications of the design with respect to the development of RF and microwave front ends. This is indispensable for the efficient utilization of frequency spectrum resources and the cost-effective enhancement of wireless system performances.

Green Communications: Digital Predistortion for Wideband RF Power Amplifiers

Abstract: The RF PA, as one of the most essential components in any wireless system, suffers from inherent nonlinearities. The output of a PA must comply with the linearity requirement specified by the standards. Due to its satisfactory linearization capability, DPD has been widely accepted as one of the fundamental units in modern and future wideband wireless systems. With the help of this flexible digital technology, the inherent linearity problem of PAs operating in the saturation region can be significantly improved, which enables us, the wireless engineers, to create more suitable RF transceiver architectures to provide wireless access with better user experience (linearity perspective) and less power waste (power efficiency perspective). This moves us one more step towards the ultimate green communications. In this article, we discussed the DPD techniques in the context of linearizing nonlinear RF PAs. As the computing-horsepower and the transistor-density of digital IC increases while the cost per transistor decreases, the concept that uses digital enhancement techniques to eliminate active analog imperfects will gain more attention from both industry and academia.

Substrate Integrated Waveguide Filters: Design Techniques and Structure Innovations

Abstract: Because of the inherent structural flexibility in coupling design and topological arrangement, substrate integrated waveguide (SIW) filter topologies enjoy better out-of-band frequency selectivity and/or in-band phase response with the allocation of finite transmission zeros (FTZs). In the first article in this series, basic design rules and fundamental electrical characteristics have been presented that indicate the superior performances of SIW structures and their filter applications. Advanced design techniques and innovative structure features have recently been reported in a large number of publications. They include cross couplings realized by physical and nonphysical paths and SIW filters with dual-mode or multimode techniques. Miniaturization-enabled techniques including low-temperature cofired ceramic (LTCC) technology have been developed and applied to the development of SIW filters to reduce the size for low-gigahertz applications using nontransverse electromagnetic (non-TEM) modes. Wideband SIW filters, multiband SIW filters, and reconfigurable SIW filters have also been reported by various research groups. This article reviews these advanced and innovative SIW filter technologies, and related examples are presented and discussed.

Near-Field Scanning Microwave Microscopy: An Emerging Research Tool for Nanoscale Metrology

Abstract: On 29 December 1959 at the annual meeting of the American Physical Society, Richard Feynman gave a lecture at the California Institute of Technology titled "There Is Plenty of Room at the Bottom: An Invitation to Enter a New Field of Physics." This memorable lecture has since become very famous as it predicted and envisioned the current era of nanoscience and nanotechnology. The atomic level represents a totally new world of fresh opportunities for design and engineering due to the new physics available at such a small scale. Feynman mentions this in his lecture, "Atoms on a small scale behave like nothing on a large scale, for they satisfy the laws of quantum mechanics" [1]. This new physics allows the manipulation of matter atom by atom. As Feynman further states, "The principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom by atom. It is not an attempt to violate any laws; it is something, in principle, that can be done; but in practice, it has not been done because we are too big" [1]. Feynman was right, and quantum mechanics continues to play a crucial role in miniaturization of technology. But advances in nanotechnology are not based purely on knowledge of the theory. Today we are realizing that all this "plenty of room at the bottom" has brought a great need for complex and ingenious metrology tools that accompany our knowledge of quantum mechanics. These metrology tools are necessary for atomic-scale manipulation as well as the characterization of each atom and its interaction with the environment. Feynman's lecture envisioned the need for significantly improved metrology tools. For example, he discussed improving the electron microscope by 100-fold. Today, in addition to the scanning electron microscope (SEM), we have the atomic force microscope (AFM), the scanning tunneling microscope (STM), and the near-field scanning optical microscope (NSOM), among many other metrology tools used for the advancement of nanotechnology [2]-[4], which Feynman did not foresee. These metrology tools also function as a platform for engineering novel atomic- and molecular-scale devices. This means performing logical operations with a single atom or molecule, manipulation of DNA molecules for information storage, or putting together nanomachines [2]-[4].

Terahertz Plasmonics: Good Results and Great Expectations

Abstract: The terahertz (THz) range is the next frontier of electronics and optoelectronics with potential applications ranging from imaging, space communications, computing, quality control, and homeland security to biotechnology and medicine. At THz frequencies, the electron inertia becomes important, providing delay between the applied voltage and electron velocity and current. When the electron collisions with impurities and lattice vibrations are infrequent, this delay leads to oscillations of the electronic density (called plasma waves) with the transistor channels serving as resonant cavities for the plasma waves. In the collision-dominated regime, the plasma waves are overdamped but still play a role by dramatically changing the electron distribution in the device channels at THz frequencies. The resonant regime can be used to generate THz radiation. Both resonant and overdamped plasma waves enable other THz electronic devices, such as detectors, mixers, and phase shifters. Periodic (symmetrical and asymmetric) plasmonic structures are especially promising for generation and detection of THz radiation. In this article, we review the state of the art of the plasma-wave electronics for silicon, III-V, III-N, and graphene semiconductor devices and project future performance of plasma-wave THz devices.

Solving the Spectrum Crisis: Intelligent, Reconfigurable Microwave Transmitter Amplifiers for Cognitive Radar

Abstract: In 2009, the U.S. Federal Communications Commission (FCC) chair, Julius Genachowski, warned of a looming spectrum crisis [1]. Issues such as a 2010 saga involving satellite communications interfering with the global positioning system (GPS)have reminded us that spectrum is becoming an ever-precious commodity. With wireless broadband technologies evolving at a rate that will outgrow the available spectrum, the U.S. government has acted to try to "stop the bleeding." President Barack Obama's National Broadband Plan of 2010 [2] mandates that 500-MHz of spectrum be reallocated for wireless broadband applications. However, the continued surge in wireless spectrum users shows that even this spectrum will be used quickly and that a new paradigm is needed. Many have suggested that dynamic spectrum access (DSA), where spectrum is assigned in real time, will be the sharing protocol of the future, and that future spectrum users will be required to be frequency-flexible and cognitive. Radar systems are spectrum users that, in their present form, will have difficulty operating in this future environment because of their fixed operating frequencies, high power, and tendency to leak power into neighboring bands and interfere with other users. In 2011, National Telecommunications and Information Administration (NTIA) Chief of Staff Thomas Power stated, "The community and policy makers must begin to understand the challenges and constraints that currently exist for radar" [3]. The last three years have witnessed an upshot of radar spectrum conferences and meetings, many organized by the NTIA and the Department of Defense's (DoD's) Joint Spectrum Center. Our interest has been stimulated through encountering this issue in military radars, and in participating as speakers and panelist in many of these meetings, including a 2011 NTIA meeting for radar and communications experts to converse about coexistence challenges. However, the DoD, the FCC, and the NTIA still have not developed any technically sound solutions to achieve spectrum sharing between radar and communications. Wireless broadband expansion is not going away. The cry to radar operators is clear: radar systems must change how they operate.

Submillimeter-Wave Radar: Solid-State System Design and Applications

Abstract: For decades, the principal role of microwave engineering techniques in the submillimeter (submm)-wave, or terahertz (THz), regime, spanning about 300 GHz-3 THz, has been to optimize the performance of components and systems used in molecular spectroscopy measurements for astronomy, earth science, and plasma diagnostics [1]. THz applications beyond spectroscopy have been much slower to develop. Ultrahigh bandwidth communication at THz frequencies may have the most powerful market forces to support it, but no systems have been deployed beyond the prototype stage, likely because of the unavailability of commercial submm-wave components, challenges with integrating them with existing communications hardware, and the often severe atmospheric attenuation.

A Dual-Frequency Ultralow-Power Efficient 0.5-g Rectenna

Abstract: The second annual Student Wireless Energy Harvesting (WEH) Design Competition was held during the 2013 IEEE Microwave Theory and Techniques Society (MTT_S) International Microwave Symposium (IMS2013) in Seattle, Washington, United States. This year, the competition parameters were modified from those of last year [1], and a new figure of merit (FoM) was established. The overall goal of the competition was to demonstrate low-mass hardware that can efficiently receive and rectify extremely low-incident power densities at two frequencies, with a fixed dc load. As the radio-frequency (RF) environment gets more saturated with spurious power, designs from this competition will become a feasible way to energize ultralow-powered or low-duty-cycle hard-to-reach sensors. Concepts such as Internet-of-Things, in which small ubiquitous devices and sensors will log data and send it to the cloud, could benefit from wireless energy harvesters. These sensors will not have convenient ways to stay powered unless power harvesting circuits are used for the sensor hardware.

Multiport Technology: The New Rise of an Old Concept

Abstract: This article provides an overview of the basics, possible applications, and specific calibration procedures for the six-port circuit, which is the most common multiport implementation of this promi ...

Implantable Antennas: A Tutorial on Design, Fabrication, and In Vitro\/In Vivo Testing

Abstract: Implantable medical devices (IMDs) are medical devices that are implanted inside the patient?s body by means of a surgical operation and can be used for a number of diagnostic, monitoring, and therapeutic applications. Typical examples include implantable pacemakers, defibrillators, glucose monitors, cochlear implants, drug infusion pumps, intracranial pressure monitors, neurostimulators, etc. [1]. To be truly beneficial while preserving patient comfort, IMDs need to wirelessly exchange data with exterior monitoring/control equipment. Low-frequency inductive links have traditionally been used for wireless telemetry of IMDs [2], [3]. However, in an attempt to overcome their inherent limitations related to low data rate, restricted communication range, and sensitivity to inter-coil misalignment, recent focus is on antenna-enabled medical telemetry for IMDs. Wireless transmission is most commonly performed in the 402?405 MHz frequency band, which has been exclusively allocated for medical implant communications systems (MICSs), is internationally available and feasible with low-power circuits, falls within a relatively low-noise portion of the spectrum, and allows for acceptable propagation through human tissue [4]. Nevertheless, other radio-frequency (RF) bands might also be used, such as those defined in the recent IEEE 802.15.6 standard [5].

High-Q Tunable Filters: Challenges and Potential

Abstract: High-Q tunable filters are in demand in both wireless and satellite applications. The need for tunability and configurability in wireless systems arises when deploying different systems that coexist geographically. Such deployments take place regularly when an operator has already installed a network and needs to add a new-generation network, for example, to add a long-term evolution (LTE) network to an existing third-generation (3G) network. The availability of tunable/reconfigurable hardware will also provide the network operator the means for efficiently managing hardware resources, while accommodating multistandards requirements and achieving network traffic/capacity optimization. Wireless systems can also benefit from tunable filter technologies in other areas; for example, installing wireless infrastructure equipment, such as a remote radio unit (RRU) on top of a 15-story high communication tower, is a very costly task. By using tunable filters, one installation can serve many years since if there is a need to change the frequency or bandwidth, it can be done through remote electronic tuning, rather than installing a new filter. Additionally, in urban areas, there is a very limited space for wireless service providers to install their base stations due to expensive real estate and/or maximum weight loading constrains on certain installation locations such as light poles or power lines. Therefore, once an installation site is acquired, it is natural for wireless service providers to use tunable filters to pack many functions, such as multistandards and multibands, into one site.

Substrate Integrated Waveguide Filters: Practical Aspects and Design Considerations

Abstract: In the current literature, the majority of research work reported on substrate integrated waveguide (SIW) filters has focused on the development of physical topologies as well as design and realization techniques for filter specifications and electrical parameters. The practical and successful implementation of SIW filters requires special consideration of mechanical and thermal properties during the design and processing stages. These properties include the effects of ambient operating environment, average, and peak power-handling capabilities as well as design and production economics, including labor costs, skilled labor availability, mass-production issues, and projected production delivery rates [1]. Bandpass filters are more concerned with those practical aspects as their in-band and out-of-band performance are much more sensitive than other types of filters to those mechanical and thermal issues.

Transversal Signal Interaction: Overview of High-Performance Wideband Bandpass Filters

Abstract: This article presents an introduction of recently wideband bandpass filters based on transversal signal interaction concepts. Different resonant structures are reported on, including branch-line coupler/ring resonator, interdigital coupled lines, DSPSL 180° phase-shifting structure, Marchand balun, open/shorted coupled lines, T-shaped structures, and open/shorted stubs. Detailed comparisons of out-of-band transmission zeros, effective circuit size, 3-dB bandwidth, upper stopband, and group delay for the wideband/UWB filters discussed in this article are presented. Different bandwidth of wideband bandpass filters can be realized based on transversal signal interaction concepts, branch-line coupler/ring resonator can be easy to realize wide bandwidth with narrow upper stopbands due to their harmonic response. The filter structures using different 180° phase-shifting structures such as DSPSL, shorted coupled lines, and Marchand balun can meet UWB bandwidth/band demand, and the circuit size can be further reduced, while the selectivity and upper stopband should be further improved. The integrated applications of shorted/open coupled lines and shorted/open stubs can increase the numbers of the transmission zeros out-of-band, besides the circuit size reduction, the upper stopband can be also extended to over 4.7 f0 . Moreover, the transversal signal-interaction concepts have been also extended to the design of differential wideband//UWB balanced bandpass filters with broadband common-mode suppression in our former works.

Measurement Techniques for RF Nanoelectronic Devices: New Equipment to Overcome the Problems of Impedance and Scale Mismatch

Abstract: The emergence of new materials (nanowires, nanotubes, graphene tapes, and thin films) and devices with nanoscale dimensions give rise to the necessity for developing dedicated techniques that will allow their electrical characterization at high-frequency range. In this article, two possible views have been highlighted to tackle the issue of the measurement of high-impedance nanoscale devices. The first solution is based on the integration of a high-impedance reflectometer and a nanoscale device on the same chip. The microwave impedance of a single CNT has been successfully measured up to 6 GHz using this technique. The second solution consists of inserting an adjustable microwave interferometer between a traditional VNA and the high-impedance device. The interferometer allows adjustment of the impedance to be measured to the highest measurement sensitivity of the measurement system. In particular, capacitances down to 0.35 fF have been measured with an error estimated to be less than 10% using the interferometric technique combined with a scanning microwave microscope. These proofs of concept on one-port nanodevices open the route towards the case of two-port active devices with high impedance. Advances in the manufacturing of next-generation nanodevices will depend on our ability to measure electrical properties and performance characteristics accurately and reproducibly at the nanoscale regime over a broad frequency range.

Tuned to Resonance: Transfer-Function-Adaptive Filters in Evanescent-Mode Cavity-Resonator Technology

Abstract: A number of promising technologies can be found today in the marketplace of reconfigurable filter ideas. They range from sub-mm-scale acoustic filters, lumped elements, two-dimensional resonators, and full three-dimensional solutions. From a system perspective, an equally diverse pool of communication, radar, electronic warfare, and sensing systems need reconfigurable filters. Despite a strong demand for such filters though, it is not easy to identify a technology that satisfies all requirements. While it is relatively straightforward to satisfy one or two important specifications such as low loss or high selectivity, it is often quite challenging to simultaneously satisfy all of them. For instance, this is particularly true when low power consumption, small form factor, and low loss become simultaneously critical decision factors. Several combinations of such factors can result in necessary design tradeoffs with no obvious solutions. Table 1 summarizes several common deciding factors in selecting a reconfigurable filter technology.

The Sky's the Limit: Key Technology and Market Trends in Satellite Communications

Abstract: The growth of demand for broadband has been seen in satellite communications as it has in other aspects of the market. Satellites carry media content around the globe, which includes satellite television, radio, and broadband services directly to consumers. Satellite communications also allows for mobile or nomadic voice and data globally. They are also critical to disaster recovery and emergency preparedness, providing critical communications following natural disasters. While the sole application of some satellites is the distribution of data, all satellites require communication systems technology. For example, remote sensing satellites may be collecting environmental data, but the data collected and the command and control of the satellite both rely on communication technology. If large amounts of data is being collected, broadband data links are required to avoid loss of data since on-board storage capacity for this data is limited.

Mitigate the Interference: Nonlinear Frequency Selective Ferrite Devices

Abstract: The linear "small-signal" properties of ferrites gave rise to several well-known microwave devices [1], [2], such as circulators, isolators, phase shifters, tunable oscillators, and tunable filters, that have had a significant impact on microwave systems following their first synthesis by Snoek [3], [4] in 1945. However, ferrites also show useful nonlinear "large-signal" properties that have been applied in power-limiter and power-enhancer devices. While these devices have not seen widespread application, their unique frequency-selective signal attenuation properties offer potential solutions to current and anticipated radiofrequency (RF) interference problems resulting from ever-increasing signal density and demands on scarce RF bandwidth.

Quick Switch: Strongly Correlated Electronic Phase Transition Systems for Cutting-Edge Microwave Devices

Abstract: The authors discuss an overview of strongly correlated electron systems and metal-insulator transition (MIT) oxide materials. Microwave applications of MIT materials are also introduced. This overview offers a vision for future microwave devices with adaptive capabilities.

Is There Anybody in There?: Intelligent Radar Occupancy Sensors

Abstract: Occupancy sensors have been used for a variety of applications over the last three decades. While initially developed for security purposes, the use of occupancy sensors has steadily extended to the control of lighting, heating, ventilation, air conditioning (HVAC), and other presence-related loads and demands in commercial and residential spaces.

Flexible Filters: Reconfigurable-Bandwidth Bandpass Planar Filters with Ultralarge Tuning Ratio

Abstract: The objective of this overview article is to report the latest research findings in the research into RF/ microwave reconfigurable-bandwidth bandpass planar filters with ultralarge passbandwidth tuning ratio. This means filtering devices with much higher flexibility, showing reconfigurable bandwidths between narrow/moderate-band and ultrawideband states. Specifically, two different solutions we recently proposed are described, with emphasis on their operating principles and achieved electrical performances. They consist of 1) transversal signal-interference switchable-bandwidth bandpass filters and 2) tune-all bandpass filters simultaneously exploiting MMRs and quality-factor control to achieve unprecedented reconfiguration levels in terms of center frequency and instantaneous passbandwidth. Some other modern filtering topologies proposed by other authors, which have clear interest to attain very high levels of bandwidth variation, are also expounded.

Quantum Sensitivity: Superconducting Quantum Interference Filter-Based Microwave Receivers

Abstract: Several critical applications of superconducting electronics that have been successfully commercialized are the Josephson voltage standard, superconducting quantum interference device (SQUID) magnetometers, superconductor-insulator-superconductor (SIS) mixers, and analog filters. More recently, digital and mixed-signal circuits based on rapid single flux quantum (RSFQ) logic have also made an impression on the high-speed/high-frequency electronics application markets.

Filling the Spectral Holes: Novel\/Future Wireless Communications and Radar Receiver Architectures

Abstract: The requirement of wireless access by novel telecommunications and remote-sensing applications, such as Internet-in-mobile services and ultrawideband (UWB) radar systems, is continuously growing in western society but also in countries with big and emerging economies such as China, Brazil, India, and even some African nations As a consequence, the radiofrequency (RF) spectrum is becoming a very valuable but scarce natural resource In relation to this, it is well known that some portions of the RF spectrum, such as those assigned to military and emergency services, remain underutilized These spectral holes, usually referred as "white spaces," then become excellent opportunities for new wireless communications and radar systems to operate Nevertheless, the necessary dynamic access to properly exploit these free spectral holes can only be performed through very sophisticated and reliable receiver architectures They must be capable of sensing very broad spectrum ranges while assuring a minimum quality for the received signals This article addresses modern RF receiver schemes for sensing widebands in communications and radar scenarios

Progress for Behavioral Challenges: A Summary of Time-domain Behavioral Modeling of RF and Microwave Subsystems

Abstract: The quest for the best compromise between the requirements for battery preservation and system operation linearity in the radio frequency (RF) and microwave front end has been a constant push for research on behavioral modeling of active devices since the early days of satellite communications [1] and has accelerated with the growth of modern mobile communication infrastructures. This focus has resulted today in a vast amount of behavioral model options, especially for the RF power amplifier (PA), in which it is not always simple for a designer to find his or her way as discussed in [2]-[5]. Using the term "behavioral model," we define these models as those derived from the observation of the electrical variables at the block ports (with very little insight on the internal composition of the block) and dedicated to the modeling of baseband/bandpass subsystems. Unlike transistor-level compact modeling, where there are well-established initiatives for model standardization driven by foundries and computer-aided design vendor companies [6], [7], there is, unfortunately, no such comparable effort yet at the subsystem level [8]. This article offers a concise summary of the recent progress on time-domain behavioral modeling with a particular focus on the continuous-time (CT) modeling theory [9].

Q-Band Millimeter-Wave Antennas: An Enabling Technology for MultiGigabit Wireless Backhaul

Abstract: The bandwidth demands in mobile communication systems are growing exponentially day by day as the number of users has increased drastically over the last five years. This mobile data explosion, together with the fixed service limitations, requires a new approach to support this increase in bandwidth demand. Solutions based on lower-frequency microwave wireless systems may be able to meet the bandwidth demand in a short term. However, with the small-cell mass deployment requiring total capacities of 1 Gb/s/km2, scalable, multigigabit backhaul systems are required. Millimeter-wave technology fits nicely into these new backhaul scenarios as it provides extended bandwidth for high-capacity links and adaptive throughput rate, which allows efficient and flexible deployment. Besides these advantages, millimeter-wave solutions become even more attractive when the cost of backhaul solutions and the cost of spectrum licenses are factored in. Compared to the cost of laying fiber to a cell base station, which is the only other scalable solution, the millimeter-wave solution becomes the most appropriate approach.

Atom Magnetism: Ferrite Circulators—Past, Present, and Future

Abstract: Magnetism, at the very fundamental level, is attributed to the circular motion of elementary charges. This occurs when electrons spin around their own axes or when they rotate around the nucleus of an atom. The combination of these two types of motion gives an atom its magnetic moment [1]. The three most significant elements from the point of view of magnetism are iron, nickel, and cobalt. Their atoms possess a large magnetic moment due to a large number of unpaired electrons in their outermost shell. They also naturally assume a crystal structure with all atoms aligned with their magnetic moments in the same direction, a configuration referred to as "ferromagnetism" [2].

From Tumor Targeting to Speech Monitoring: Accurate Respiratory Monitoring Using Medical Continuous-Wave Radar Sensors

Abstract: Using microwaves to detect small physiological movements such as respiration and heartbeat dates back to the 1970s [1]. It is realized by detecting the phase information in the received radar signals, which is caused by Doppler shift due to the moving chest wall. The principle is similar to the radar guns used by police officers to detect over-speed vehicles. Based on the form of the transmit signal, there are basically two types of radars: continuous-wave (CW) radar and ultrawideband (UWB) radar. The CW radar falls into three subcategories: single-tone, stepped frequency (SFCW), and frequency-modulated CW (FMCW). Each category of radars has its specific advantages. The singletone CW radar has a simple system architecture that allows high-level chip integration [2]?[4]. It also has high accuracy (submillimeter) in relative displacement measurement [5]?[6]. Unfortunately, because no instant bandwidth is transmitted, single-tone CW radars do not carry range (i.e., absolute distance between the radar and the subject) information. FMCW radars are able to detect range information [7]?[8] but normally require a very large bandwidth and more sophisticated signal processing to realize high-accuracy relative displacement measurement. Researchers also have successfully integrated the FMCW radar on silicon chips [9]?[11]. SFCW radars carry some advantages of both singletone CW radars and FMCW radars and thus have been successfully used in applications such as fall detection [23]. In addition, a hybrid radar system combining the advantages of the single-tone and FMCW radars was reported in [12]. UWB biomedical radars have veryhigh-range resolution due to its wideband nature [13]. The state of the art shows that UWB pulse radars have been efficiently implemented on silicon [74] and have been successfully applied to the accurate detection of respiratory rate and apnea in adults and infants [75].

Hassle-Free Vitals: BioWireleSS for a Patient-Centric Health-Care Paradigm

Abstract: Continuous monitoring of vital information via a wireless medium has become an integral part of next-generation health-care technologies. The benefits of a wireless monitoring technique include facilitating in-home care services, reduction of the cost of frequent visits to hospitals, and lightening of the burden to the elderly persons. The development of miniature, lightweight, and energy-efficient circuit solutions for biomedical sensor applications has been made possible by the tremendous recent advancements in health-care monitoring technologies, micro- and nanofabrication processes, and wireless communications. Exuberant growth of the wireless sensor networks has opened up a new and innovative application of wireless technology in health care. The advancement of wireless technology has led to the development of the recently proposed comprehensive patient monitoring systems such as wireless body area network (WBAN) and body sensor network (BSN). Implantable and wearable sensors are integral components of these networks and are employed for monitoring various levels of physiological activities. Wireless sensor technology provides an effective tool for instant access to patient data, laboratory test results, and clinical histories as well as insurance information, thereby ensuring immediate health care in case of emergency, eliminating the lengthy clinical decision. This biomedical wireless technology has resulted in a new health-care concept known as telemedicine, which facilitates the monitoring of in-home patient care by incorporating smart medical devices and WBANs. In this scheme, implantable and wearable sensors are placed within the vicinity of the patient's body and various physiological parameters are monitored and transmitted wirelessly to a nearby hub station and subsequently to the remote health-care provider via a secure wireless communication network. The telemedicine platform can also be configured for identification of the object location, medicine reminder, or emergency alert in case of any sign of fatal disease. As a result of the recent developments in biomedical wireless technologies, the traditional clinic-centric health care is giving way to a patient-care centric health-care concept. This translational health-care concept facilitates the multidirectional integration of basic research, patient-oriented research, and population-based research, with the long-term aim of improving the health of the public. However, the successful integration of this new health-care paradigm hinges on the proper interpretation, storage, and dissemination of the large data sets generated by the all implantable and wearable devices within the wireless network.

The Sound the Air Makes: High-Performance Tunable Filters Based on Air-Cavity Resonators

Abstract: Tunable filters have a wide range of applications from software-defined radio to reconfigurable satellite payloads. They are a key building block for any flexible transceivers. A variety of tunable filter technologies can be found in the literature. Examples include: planar tunable filters employing solid-state or microelectromechanical systems (MEMS) varactors [1]-[6], and ferroelectric variable capacitor tuned coaxial filters [7]. The choice of technology is driven by the application. In this article, we focus on applications requiring high performance, including low loss, high-power handling capability, and high stability, mainly for communications satellites or wireless base stations. These requirements immediately rule out any low-quality factor (Q) technologies. For instance, besides low Q, planar-type tunable filters typically suffer from poor selectivity and transmission-response variation over the tuning range. Technologies based on substrate-integrated-waveguide (SIW) offer better Q than microstrip circuits and advantage in packaging [8]-[10]. However, in most cases, their Q is comparable to strip-line circuits with the same volume. Air-cavity resonators, on the other hand, offer high-Q in the range of thousands to tens of thousands and high-power handling and are therefore one of the obvious choices. The addition of each requirement, such as power, selectivity, vibration, and temperature stability, further limits available choices. We are not aware of an existing technology that satisfies all these requirements. The search for a viable solution for the targeted high-end applications is indeed a difficult journey, with years of experience accumulation from past good and bad designs.

Linear and Efficient Doherty PA Revisited

Abstract: Designing a simultaneously linear and efficient radio-frequency (RF) power amplifier (PA) is no simple task. The Microwave Theory and Techniques Technical Committee on The High Power Amplifier Components (MTT-5), aiming to promote this challenge at the student level, organized the ninth version of its annual high efficiency PA contest at the 2013 IEEE Microwave Theory and Techniques Society (MTT-S) International Microwave Symposium (IMS2013). Built upon our participation in 2012, the 3.5-GHz linear Doherty PA design was only slightly modified in response to a change in the gain requirement of this year's competition rules.